1. Field of Invention
The invention relates to a hydraulic control apparatus for an automatic transmission.
2. Description of Related Art
Conventionally, an automatic transmission used for a vehicle, such as automobile, has been provided in which a change gear apparatus provided with a planetary gear unit or the like is included, the change gear apparatus comprising a plurality of friction engagement elements, such as a clutch, a brake, and the like, and a plurality of speeds are achieved by selectively outputting revolutions from the gear elements, such as a sun gear, a ring gear, a carrier and the like of the planetary gear unit, by engaging and disengaging respective friction engagement elements in a predetermined combination.
The friction engagement elements are engaged and disengaged by operating a hydraulic servo in a hydraulic circuit. The hydraulic servo comprises a hydraulic servo drum having an outer circumferential wall and an inner circumferential wall, an annular piston slidably fitted in the hydraulic servo drum, and the like. The friction engagement element disposed opposite to the annular piston is engaged and disengaged through the movement of the annular piston by supplying oil to an apply oil chamber defined between the hydraulic servo drum and the annular piston.
Moreover, various solenoid valves, a switching valve and the like are disposed in the hydraulic circuit, and a predetermined switching valve is switched over. The hydraulic servo connected with the switching valve is supplied with hydraulic pressure, by turning ON and OFF a solenoid of a predetermined solenoid valve.
In an automatic transmission of the above structure, one or more predetermined friction engagement elements are engaged in the case of achieving a certain speed; however, the change gear apparatus interlocks, when a failure (abnormality) is generated in the solenoid valve and a friction engagement element not required to be engaged is engaged.
Therefore, there is provided an hydraulic circuit for preventing the change gear apparatus from interlocking, when the hydraulic servo of the friction engagement element not required to be engaged is supplied with hydraulic pressure, by switching over a predetermined switching valve by the hydraulic pressure, and stopping hydraulic pressure supply to the hydraulic servo of the friction engagement element (refer to the Japanese Patent Application Laid-Open No. 63-210443).
The conventional hydraulic circuit can prevent the change gear apparatus from interlocking when a friction engagement element not required to be engaged is engaged, that is, in a failed state where the hydraulic servo is supplied with hydraulic pressure. However, when a friction engagement element required to be engaged is not engaged, that is, in a failed state where the hydraulic servo is not supplied with hydraulic pressure, depending on the type of automatic transmission, there is the possibility that a neutral state is formed in the gear change, power can not be transmitted through the gear change, and not only an intended gear change can not be realized appropriately, but also the vehicle can not run.
It is an object of the invention to solve the problem of the conventional hydraulic circuit, to provide a hydraulic control apparatus for automatic transmission that can prevent a neutral state from being formed in the gear change, and to perform an intended gear change appropriately.
To achieve the aforementioned object, the hydraulic control apparatus for an automatic transmission in accordance with the invention comprises a plurality of hydraulic servos engaging and disengaging respectively a plurality of friction engagement elements; hydraulic pressure supply means for supplying a hydraulic servo of a predetermined friction engagement element selected in correspondence to a speed to be achieved with hydraulic pressure; and auxiliary hydraulic pressure supply means for supplying a predetermined hydraulic servo with a hydraulic pressure other than the hydraulic pressure generated by the hydraulic pressure supply means, in the case that the hydraulic pressure supply means is placed in a first unsupplied state (failed state) where the hydraulic pressure supply means can not supply the hydraulic servo of the predetermined friction engagement element with hydraulic pressure.
Moreover, the auxiliary hydraulic pressure supply means does not supply the predetermined hydraulic servo with the other hydraulic pressure, in the case that the hydraulic pressure supply means is placed in a second unsupplied state (under underlap control) where the hydraulic pressure supply means does not supply the hydraulic servo of the predetermined friction engagement element with hydraulic pressure.
In this case, when the hydraulic pressure supply means is placed in the first unsupplied state where the hydraulic pressure supply means can not supply the hydraulic servo of the predetermined friction engagement element with hydraulic pressure, the predetermined hydraulic servo is supplied with a hydraulic pressure other than the hydraulic pressure generated by the hydraulic pressure supply means. Therefore, a predetermined speed can be achieved, preventing a neutral state from being formed in the change gear apparatus.
On the other hand, when the hydraulic pressure supply means is placed in a second unsupplied state where the hydraulic pressure supply means does not supply the hydraulic servo of the predetermined friction engagement element with hydraulic pressure, the another hydraulic pressure is not supplied to the predetermined hydraulic servo. Accordingly, the underlap control can be performed, and the intended gear change can be performed appropriately.
In another hydraulic control apparatus for an automatic transmission in accordance with the invention, further, the hydraulic pressure supply means is put in the second unsupplied state (under underlap control) during a predetermined gear change (during gear change under underlap control).
In still another hydraulic control apparatus for automatic transmission in accordance with the invention, further, the auxiliary hydraulic pressure supply means is failsafe means, and provided with switching means for not supplying the predetermined hydraulic servo with the other hydraulic pressure during a predetermined gear change (during gear change under underlap control).
In still another hydraulic control apparatus for automatic transmission in accordance with the invention, further, the predetermined friction engagement elements are two friction engagement elements, forming a state allowing transmitting of power in the gear change by engaging the two friction engagement elements.
Moreover, the auxiliary hydraulic pressure supply means is provided with hydraulic pressure generation detection means for detecting generation of hydraulic pressure to be supplied to the hydraulic servo of at least one of the two friction engagement elements. Then, the other hydraulic pressure is not supplied to the predetermined hydraulic servo, in the case of detection of generation of the hydraulic pressure.
Still another hydraulic control apparatus for automatic transmission in accordance with the invention, comprises a plurality of friction engagement elements; a plurality of hydraulic servos engaging and disengaging respectively the plurality of friction engagement elements; hydraulic pressure supply means for generating a predetermined hydraulic pressure, and supplying the predetermined hydraulic pressure to the hydraulic servo of the predetermined friction engagement element selected in correspondence to a speed to be achieved; a switching valve including an input section where the hydraulic pressure generated by the hydraulic pressure supply means is input and an output section for outputting a hydraulic pressure other than the hydraulic pressure generated by the hydraulic pressure supply means in order to supply to the predetermined hydraulic servo; and valve switching means for further switching over the switching valve in a state where there is no hydraulic pressure input to the input section, and the switching valve switches over to output the other hydraulic pressure.
In this case, when the hydraulic pressure is not input into the input section, the switching valve is switched over to output another hydraulic pressure; the valve switching means further switches over the switching valve in this state. Therefore, the predetermined speed corresponding to the hydraulic servo can be achieved, by supplying the hydraulic pressure to the predetermined hydraulic servo, thereby preventing the neutral state from being formed in the change gear apparatus.
Moreover, if the valve switching means further switches over the switching valve, the another hydraulic pressure is not supplied to the predetermined hydraulic servo. Therefore, the underlap control can be performed, and the intended gear change can be performed.
In still another hydraulic control apparatus for automatic transmission in accordance with the invention, further, the predetermined friction engagement elements are two friction engagement elements. And, a state allowing transmitting of power in the change gear apparatus is formed by engaging the two friction engagement elements.
Moreover, the hydraulic pressure to be supplied to the hydraulic servo of the two friction engagement elements is input to the input section.
In still another hydraulic control apparatus for automatic transmission in accordance with the invention, further, the switching valve is provided with countering means against the hydraulic pressure input to the input section, and generating a counter force against the switching force with which the valve switching means switches over the switching valve.
Still another hydraulic control apparatus for automatic transmission in accordance with the invention further has another friction engagement element than the two friction engagement elements.
In addition, the switching valve is provided with a hydraulic pressure supply detection section for detecting a simultaneous supply of hydraulic pressure to be supplied to the two friction engagement elements and the hydraulic servo of the another friction engagement element; and a section not supplied with hydraulic pressure for not supplying the hydraulic servo of the another friction engagement element upon detection of the simultaneous supply of hydraulic pressure to be supplied to the two friction engagement elements and the hydraulic servo of the another friction engagement element.
In this case, when the hydraulic pressure to be supplied to the hydraulic servo of the two friction engagement elements and the another friction engagement element at the same time, the hydraulic pressure is not supplied to the hydraulic servo of the another friction engagement element, thereby preventing the change gear apparatus from interlocking.
Still another hydraulic control apparatus for automatic transmission in accordance with the invention further comprises a switching control valve that is provided with a first input section to which the hydraulic pressure to be supplied to the hydraulic servo of the predetermined friction engagement element is input, and a second input section to which the hydraulic pressure to be supplied to the hydraulic servo of the another friction engagement element is input, for generating a signal hydraulic pressure to be supplied to the switching valve when the hydraulic pressure to be supplied to the hydraulic servo of the predetermined friction engagement element, and the hydraulic pressure to be supplied to the hydraulic servo of the another friction engagement element are input to the first and second input sections.